1. Field of the Invention
The present invention concerns a radiology installation with compensating filter(s) and relates, more particularly, to novel positioning means for such a filter.
2. Summary of the Prior Art
It is known that in a radiology installation, the differences of thickness and density of the portion of the patient who is in the X-ray field are sometimes such that the "modulation" of the beam by the subject exceeds the dynamics of the detector. It is known to interpose structures having determined shapes and thickness in function, especially, of the nature (average density) of the tissues above which they must be placed. These compensating structures or filters comprising elements whose positions are adjustable have, for many years, been made of aluminum. More recently, filters made of transparent plastic material loaded with lead have been proposed, which solution allows, in particular, to maintain the luminous positioning beam (symbolizing the X-ray beam) during positioning and adjustment of the filters. Nevertheless, the efficiency of these adjustments depends largely on the skill of the operator at least for carrying them out in radioscopic mode, which presents other drawbacks. Indeed, on the one hand, the patient is subjected to a further exposure to irradiation, which is not directly useful to the diagnosis, while, on the other hand, during the length of service the operator often has his hands and forearms directly exposed to the X-ray beam.
The present invention aims at least to allow a more accurate and more rapid positioning of the compensating filter(s). It also aims at reducing as much as possible the irradiation doses received by both the patient and the operator.
With this purpose, the invention principally concerns a radiology installation, comprising an X-ray source, a receiver and at least one adjustable compensating filter, normally placed within the volume in which is inscribed the X-ray beam, wherein it comprises optical means for projecting a radiological image established by the said receiver and means for placing the said filter, at least during an adjustment phase, within the volume in which is inscribed the said beam of the said image and wherein the said compensating filter has partial absorption properties both in the field of X-rays and in the field of visible light.
According to one possible embodiment, the installation comprises means for deflecting the beam of the image, these means being disposed so that a portion of the volume in which the said beam of the said image is inscribed substantially coincides with a portion of the volume in which the said X-ray beam is inscribed, the filter being situated within this common portion of the volume.
In the majority of modern radiology installations, an image memory is interconnected between the detector (generally a luminance or brightness amplifier) and visualization means. In order to solve completely the frequent irradiation problem of the operator, it is possible to use this memory within the framework of the present invention.
More precisely, the invention also concerns an installation of the type mentioned herein-above comprising an image memory connected to the said receiver so as to memorize a series of digital data that is representative of a radiological image, the said memory being of the cyclical and autonomous reading type, wherein a video projector having its signal input connected to the output of the said memory is disposed so that its axis of optical projection is substantially perpendicular to the axis of the X-ray beam and wherein a mirror is interposed in the volume within which the said X-ray beam is inscribed at 45.degree. with respect to the said optical proection axis.
Therefore, a pulsated emission of the X-ray source, having a relatively short duration, is sufficient to register in the memory the representative data of a radiological image, which is then projected onto the patient's body (or on to a screen placed upon him) which allows to adjust the position of the compensating filter without requiring the presence of an X-ray beam.
In the case where, for example, a monochromatic radiological image is projected upon the patient, a correct adjustment of the filter is obtained when the projected image has relatively slight contrasts.